Dark field color filter with polarizing means for microscopes



April 29, 1952 K. A. FISCHER 2,594,758

DARK FIELD COLOR FILTER WITH POLARIZING MEANS FOR MICROSCOPES Filed Jan. 18, 1949 f ENTOR. ar /l/c e V /fffmwfy Y Patented pr. 29, i952 UNI TE D S TAT E S PAT ENT 'OF FICE DARK HELD COLOR FILTER WITH'FOLAR- IZING MEANS FOR -MICROSCOPES Karl A. Fischer, Washington, D. C. Application January -18, .1-949, vSerial No. 371,522

('Cl. '18K-40) (Granted under the act of -March 3, 1883, as amended April 30, 1928-; =370 0. G. 757,-)

11 Claims.

"The invention described fheren, if zpatented, m'a'y -b'e l'xna'nufa'ctured :and used vby `or for `the Government Yfor governmental .purposes without f'th'e `pa'yment t'o me lof .'any royalty thereon.

"Tli'i'si-nvention relates to am'ethod and-'apparatus ffo'r' illuminatingl an object with a r combina- 'Y'of polarized A"colored light and different or v7complem'entaryfnonpcilarized -colored lig-ht. More particularly, theiinvention relates to anlimproved microscope and itil-ter 'fo'r simultaneous dark viield examination Soif foptically active and optically inactive materials, as 'crystals vor the like, .also permitting distinction fof positive. and negative double ref-ra'ctivity.

In lthe field fof 'microscopic examination it has heretofore been the practice to provide a conidenser mounting 'with a special diaphragm, or diaphragms, of contrastingly colored openings -to "show Vthe 'objectiveina bright color 'against an inte'n'sely but 'differently colored .background By these devices of optical coloring, simultaneous discernment Iof `optically ra'ctive and linactive -mateials with distinction between positive 'and negative double refractivity cannot be determined. vlliurthe'r, it A'has 'been fou-nd that when .polarized 1Wl-iite lig-ht and Ynonpolarized vcolored light `are utilized in the manner aspspecilcally 'disclosed -inmy :co-.pending application, Serial No. 26,911, filed May, 13,1948, that yalthough optically active objects fstandf'out against colored inactive material, they are, in some instances, overillumi- -nated o'r too bright, 'and the Adesirable effect of showing, `cracks and inclosures in v-contrasting c'olor may be suppressed.

.-It.^is, therefore, :an'object of this invention to prov-ide azmicroscope with dark lfield illumination .-for discernment of -isotropic material and nonvisotropic ymaterial lwith 'distinction between positivve and negativel double reiractivity `Anadditionalobject of this invention is to y.provide 1a lens "and improved filter therefor for illumination of'an object with polarized colored light and non-polarized Acolored :light in combination.

AfItis another-object of this invention to provide fanfi-mproved multicolored light filtering device, usi-ng .polarized coloredand non-polarized colored llight :for simultaneous color illuminating `of doubly vrefractingoptically Aactive and optically inactive materials in -a dark field background.

Itis Aa A'further' object -of this invention .to provide-an improved 'illumination vof voptically active yand inactive'crystals with clear ldiscernment of `Apositive or Enegative double refractivity in cleai outline vagainsta dark background, with a clear 'showing of their depth, cracks and edges in contrasting Vcolors of converging `colored -light beams.

Allthe further objects and advantages of this invention will be apparent from the following description, when taken' in conjunction with the following drawings, wherein:

`Figure 1 is a front elevation of a microscope arrangement Figure 2 is a cross-sectional view illustrating an vembodiment of my improved vfilter; and

Figure 3 is a top plan View of Figure 2.

Referring to the drawings, a conventional microscope condenser mounting It is diagrammatically illustrated for holding lenses II and I2, which direct light to an object on the slide I3 under cover glass I4 and to the objective 'lens piece I5 Which contains an analyzer foil I5. `Beneath the lens I Ithe condenser mounting AIIJ lcarr-ies the usual diaphragm I6 and also the usual 'support or holder II for insertion of my improved filter I3. The lter I8, as illustrated, may be held within the support I'I by holdingring "I9, mounted as described herein, or by other suitable and conventional holding means as desired. "Such means, for example, may be an adjustable mounting in the nature of that disclosed by E. S. Bissell in Patent Number 2,083,820 or Roesch Patent Number 2,105,671.

The lter I8 isan annular member, formed of non-transparent diaphragm 29 secured to transparent colored foil 2l, Athrough both of which is provided a central opening 22. Positioned or secured beneath the opening 22 is a polarizing film of sheet material 23 or other polarizing body and a ycolored foil 24. The colored foil 24 is positioned intermediate Aof the polarizing film 23 and -a light source I0 of a conventional character, `as generally utilized for microscopic exammations. This ilter member I8 is adapted to rest upon the flange I9 of ring member I9 which is insertable Within the support Il, and Aheld therein by the obvious screw threads 25, -With polarizing iilm 23 in crossed position -to analyzer film I5'.

`For ypurposes of illustration, inthe nlter structure as described, the colored foil 2| is red and the colored vfoil 24 `is a transparent green `or -blue,'thereby causing projected non-polarized red lightand polarized green or blue light to pass into condensers II and I2 to converge upon an object supported by plate I3. The effect produced upon an object, as paranin crystals or the like, is to obtain a distinct picture of active or nonisotropic and inactive or isotropic crystals in the colors ofthe polarized-and unpolarized lights respectively on a perfectly dark background. If, in addition, a first order red plate (also called gypsum plate) is used the active crystals stand out in blue-green or in yellow-green, according to their positive or negative double refractivity. Further, the converging light beams show edges and inactive material in bright red. The condenser lens system Il, l2 is positioned intermediate the analyzer I5 on the one hand and the diaphragm and contrasting non-polarizing and polarizing filters in retaining ring I9 on the other hand; all of the foregoing optical members are aligned on the same optical axis.

In the apparatus described, although polarizing prisms are not excluded, the use of polarizing foils is advantageous in that these foils do not polarize the long wave red light components which causes the purple color between crossed foils. polarized beam eliminates or reduces this long wave component and the remaining wave lengths are well polarized and give a dark background.

As indicated, a blue foil may be substituted for the green foil 24 for use Vwith a red foil 2|. The

foils may not be reversed in color arrangement as the advantage of eliminating the non-polarized purple component of the polarized central beam would be lost. That is, a short wave central color filter is essential. For the converging non-polarized color beams other color filters as orange or amber may be substituted for the color foil 2l. Further, it is evident that any color combination can be used, in the event that the central beam is fully polarized by prisms or the like.

l Generally it may be indicated that an adaptation of the colored light distribution, as herein described, can also be used to control optical col` oring in known procedures wherein it is evident that the position of the polarizing films to each other need not necessarily be crossed. In such instances some light from the colored central beam will enter the condensing lens directly and cause a colored background, more or less bright,

The green or blue filter for the central.

according to the position of the polarizing foils.

' side inactive materials diminishes gradually as the Polaroid foils or prisms, if used, deviate from crossed position.

In accordance with the patent statutes, I have described in detail what I now consider to be the preferred form of the inventon, but it will be obvious that various minor changes may be made in the structural details without departing from the spirit of the invention; and it is intended that all Such changes be included Within the scope of the appended claims.

I claim:

l. A composite light filter structure comprising a centrally apertured opaque annular diaphragm, an annular transparent nonepolarizing color filter having a central aperture and concentric with said opaque annular diaphragm, the efective area of said annular color filter being contiguous to said opaque annular diaphragm, and a circular transparent filter of a contrasting color aligned with the central aperture of said opaque annular diaphragm, said circular filter including a light polarizing means and the effective area of said circular filter being out of register with the effective area of said annular non-polarizing color filter, said circular filter and the central apertures of said opaque annular diaphragm and of said annular non-polarizing color filter being aligned on the same optical axis; whereby colored non-polarized light and contrastingly colored polarized light may be separately and simultane- 4 ously transmitted through a condenser lens onto a microscope dark field and whereby optically active and inactive material may be simultaneously observed in contrasting colors in said dark field.

2. A composite light filter structure comprising a centrally apertured opaque annular diaphragm, an annular transparent non-polarizing color filter having a central aperture and concentric with said opaque diaphragm, the color of said nonpolarizing filter having a wave length exceeding the wave length of green and the effective area of said annular color filter being contiguous to said opaque annular diaphragm, and a circular transparent filter of a contrasting color having a short wave length not exceeding the wave length of green, said circular filter being aligned with the central aperture of said opaque annular diaphragm and including light polarizing means, and the effective area of said circular filter being out of register with the effective area oi said annular non-polarizing color filter, said circular filter and the central apertures of said opaque annular dia- 4phragm and of said annular non-polarizing color filter being aligned on the same optical axis; whereby colored non-polarized light and contrastingly colored polarized light may be separately and simultaneously transmitted through a condenser lens onto a microscope dark field and whereby optically active and inactive 4material may be simultaneously observed in contrasting colors in said dark field.

3. A composite light filter structure according to claim 2, wherein the color of said annular nonpolarizing color filter is red.

4. A composite light filter structure according to claim 2, wherein the color of said circular filter is blue.

5. A composite light filter structure according to claim 2, wherein the color of said circular filter is green.

6. A composite light filter structure comprising a centrally apertured opaque annular diaphragm and a centrally apertured annular transparent non-polarizing color filter surrounding said diaphragm, the effective area of said annular filter being contiguous to the outer peripheryof said opaque annular diaphragm, and a circular transparent filter or" a contrasting color'aligned with the central aperture of said opaque annular diaphragm, said circular filter including light polarizing means and the effective area of said circular filter being out of register'with the effective area of said annular non-polarizing color filter, said circular filter and the central apertures of said opaque annular diaphragm and of said annular non-polarizing color filter `being aligned on the same optical axis; whereby colored non-polarized light and contrastingly colored polarized light may be separately and simultaneously transmitted through a condenser lens onto a microscope dark field and whereby optically active and inactive material may be simultaneously observed in contrasting colors in said dark field.

7. VA composite light filter structure comprising a centrally apertured opaque annular diaphragm ,and a centrally apertured annular transparent non-polarizing color filter surrounding said diaphragm, the color of said non-polarizing filter having a wave length exceeding the wave length of green and the effective area of said annular color iilter being contiguous to the outer periphery of said opaque annular diaphragm, and a cirl cular transparent filter of a contrasting color aligned with the central aperture of said opaque annular diaphragm, said circular filter including light polarizing means and the effective area of said circular filter being out of register with the effective area of said annular non-polarizing color iiltensaid circular filter and the central apertures of said opaque annular diaphragm and of said annular non-polarizing color filter being aligned on thesame optical axis; whereby colored non-polarized light and contrastingly colored polarized light may be separately and simultaneously transmitted through a condenser lens onto a microscope dark field and whereby optically active and inactive material may be simultaneously observed in contrasting colors in said dark field.

8. A composite light filter structure comprising a retaining ring, a centrally apertured annular light transmitting non-polarizing color filter member mounted in said retaining ring, and a centrally apertured opaque diaphragm of a lesser outer diameter than said non-polarizing color filter and a circular light transmitting filter or a contrasting color mounted on said annular nonpolarizing color iilter, said circular filter including light polarizing means, the diameter cf said circular polarizing color filter not exceeding the diameter of said annular diaphragm, the effective areas of said diaphragm and color filters being concentric, the effective area of said circular color filter being out of register with the effective area of said annular non-polarizing color lter,

land the effective area of said opaque diaphragm being an annular zone positioned between the effective areas of said circular color filter and of said annular non-polarizing color filter; whereby said composite filter structure may be unitarily mounted on a" microscope in a position adjacent the condenser lens of said microscope, and whereby colored non-polarized light and contrastingly colored polarized light may be separately and simultaneously transmitted through said condenser lens onto a dark field for the simultaneous observation of optically active and inactive materialin contrasting colors.

9.1A composite light filter structure according to claim 8, wherein vthe color of said non-polarizing color filter has a wave length exceeding the Wave length of green, and wherein said circular' filter has a contrasting color having a short wave length not exceeding the wave length of green.

10. In combination with a microscope having a condenser lens and an analyzer aligned on an optical axis; a centrally apertured opaque annular diaphragm, an annular transparent nonpolarizing color filter having a central aperture and concentric with said opaque annular diaphragm, the effective area of said annular color filter being contiguouus to said annular diaphragm, and a circular transparent lter of a contrasting color aligned with the centralaperture of said opaque annular diaphragm, said circular filter including light polarizing means and f the effective area of said circular filter being out of register with the effective area of said annular non-polarizing color filter, said circular filter kand the central apertures of said opaque annular diaphragm and of said annular non-polarizing color filter being aligned on said optical axis, said condenser lens being positioned intermediate said analyzer on the one hand and said opaque annular diaphragm, annular non-polarizing color filter and contrasting circular color filter on the other hand; whereby colored non-polarized light and contrastingly colored polarized light are separately and simultaneously transmitted through said condenser lens onto a dark field and whereby optically active and inactive material may be simultaneously observed through said analyzer in contrasting colors in said dark eld.

1l. In combination with a microscope having a condenser lens and an analyzer aligned on an optical axis; a centrally apertured opaque annular diaphragm, an annular transparent nonpolarizing color filter having a central aperture and concentric with 'said opaque annular diaphragm, the color of said non-polarizing filter having a wave length exceeding the wave length of green, the effective area of said annular color filter being contiguous to said annular diaphragm, and a circular transparent filter of a contrasting color of a short wave length not exceeding the wave length of green, said circular filter being aligned with the central aperture of said opaque annular diaphragm and including light polarizing means, the effective area of said circular filter being out of register with the effective area of said annular non-polarizing color filter, said circular filter and the central apertures of said opaque annular diaphragm and of said annular non-polarizing color filter being aligned on said optical axis, said condenser lens being positioned intermediate said analyzer on the one hand and said opaque annular diaphragm, annular non-polarizing color filter and contrasting circular color filter on the other hand; whereby colored non-polarized light and contrastingly colored polarized light are separately and simultanegusly transmitted through said condenser lens onto a dark field and where- -by optically active and inactive material may be simultaneously observed through said analyzer in contrasting colors in said dark field.

KARL A. FISCHER.

REFERENCES CITED The following references are of record 'in the file of this patent: Y

UNITED STATES PATENTS Number Name Date 793,970 Wanner July 4, 1905 1,225,250 Ingersoll May 8, 1917 1,887,099 Kraft Nov. 8, 1932 2,097,762 Heine Nov. 2, 1937 2,105,671 Roesch Jan. 18, 1938 2,475,921 Smith July 12, 1949 OTHER REFERENCES Powell, Practical Photomicrography, article in Photo-Technique, pages 9 and 13 cited, December 1939, published by McGraw-Hill Publishing Co., New York, New York (Photocopy in Division 7). 

